Prehistoric World

Sahelanthropus tchadensis: More Likely
Human

BBC News, 6 April 2005

Experts are a step closer to answering whether an ancient skull
from Africa belonged to a possible human ancestor or to a creature
closer to apes.

Fresh fossil finds from Chad in central Africa, as well as a new
analysis of the skull, seem to confirm "Toumaļ" was closer to us.
The Toumaļ specimen was unearthed in Chad in 2002 to international
acclaim. But rival researchers attacked claims by the discovery team
that it was the oldest hominid, or human-like creature.

The near-complete skull, pieces of jawbone and several teeth
unveiled in 2002 were found in the desert of northern Chad by a team
led by Michel Brunet, at the University of Poitiers, France.

At six to seven million years old, Sahelanthropus tchadensis,
(better known by its nickname Toumaļ), dates to about the time
where, according to genetic data, the ancestors of humans and the
ancestors of chimpanzees went their separate evolutionary ways.

The find had a puzzling combination of modern and primitive
features, with an ape-like brain size and skull shape, combined with
a more human-like face and teeth. It also sported a remarkably large
brow-ridge, more similar to that of hominids.

But at least one anthropologist argued that the fossil could
belong to a female forerunner of the gorilla.

Now Brunet and colleagues report discovering two new jaw
fragments and the crown of a tooth in the same geographical area as
the earlier fossils. The authors say their analysis reveals key
similarities to hominid fossils and differences from African apes
that support the idea Toumaļ was a hominid.

In a separate paper, a team including Brunet and Christoph
Zollikofer of the University of Zurich in Switzerland, presents a 3D
computer reconstruction of the skull, which had been badly distorted
in the ground.

The team has essentially "unmangled" the skull, and the
reconstruction appears to confirm that tchadensis shared key
features with later hominids.

In addition, the position of the foramen magnum - the hole where
the spinal cord enters - is similar to that in humans but not apes.
This suggests Toumaļ was bipedal; the creature walked upright like
modern humans.

"We performed a virtual reconstruction because the skull is
heavily mineralised and distorted. It is impossible to do one by
physical means," Professor Zollikofer said. "[The find] is
absolutely unique for several reasons. First, because of its age.
Then because of its geographical location. Third, because it is
incredibly complete."

Not swayed

Martin Pickford, of the National Museum of Natural History in
Paris, is one of those scientists unconvinced by arguments that
Toumaļ is a hominid.

"What we're saying is that it is an ape-like animal. It may well
have given rise to bipedal hominids, but it's not yet a bipedal
hominid," Dr Pickford said.

Professor Zollikofer commented: "I would say most of the
disagreement over the fossil came from the fact that it is
distorted, so it is quite difficult to recognise the diagnostic
hominid features."

If Toumaļ really does belong on the human branch of the
evolutionary tree, its discovery calls into question certain
assumptions about our prehistory. The fossils were found some
2,500km (1,500 miles) west of the African Great Rift Valley -
traditionally seen as humankind's ancestral home due to the wealth
of hominid fossils that have been discovered there.

The discovery of tchadensis implies early hominids ranged
far wider from East Africa, and far earlier, than previously
thought. It also suggests that hominids evolved quickly when they
set off on their own evolutionary path.